1. Field of the Invention
The present invention relates to a double window processing device for a television system, and more particularly to a double window processing device for a television system adopting multiple color systems which can improve the picture quality by matching the synchronization of a sub-channel picture with that of a main-channel picture.
2. Description of the Related Art
A conventional double window processing device for a television system, as shown in FIG. 1, includes main-channel and sub-channel tuners 101 and 104 for receiving radio frequency (RF) signals received through an antenna ANT, and outputting main-channel and sub-channel intermediate frequency (IF) signals, respectively, main-channel and sub-channel IF processing sections 102 and 105 for processing IF output signals of the main-channel and sub-channel tuners 101 and 104, and outputting composite video signals CVBS1 and CVBS2, respectively, a digital comb filter 103 for separating the composite video signal CVBS1 from the main-channel IF processing section 102 into a luminance signal Y.sub.M and a chrominance signal C.sub.M, a double window processing section 106 for separating the composite video signal CVBS2 from the sub-channel IF processing section 105 into a luminance signal Y.sub.P and a chrominance signal C.sub.P, a luminance/chrominance (Y/C) switching section 107 for switching the luminance and chrominance signals YM and CM from the digital comb filter 103 and the luminance and chrominance signals Y.sub.P and C.sub.P from the double window processing section 106, and outputting a final luminance signal Y and chrominance signal C, and a video processing section 108 for receiving the luminance and chrominance signals Y and C from the Y/C switching section 107, and outputting color signals of red (R), green (G), and blue (B) to a color picture tube (CPT).
The operation of the conventional double window processing device as constructed above will now be explained.
RF signals of the NTSC-M and FAL-M,N systems are inputted to the tuner 101 through the antenna ANT, and the turner 101 outputs the IF signal IF1 to the main-channel IF processing section 102.
The main-channel IF processing section 102 processes the IF signal IF1, and outputs the composite video signal CVBS1 to the digital comb filter 103. Accordingly, the digital comb filter 103 separates the composite video signal CVBS1 into the luminance signal Y.sub.M and the chrominance signal C.sub.M.
The Y/C switching section 107 switches the luminance signal Y.sub.M and the chrominance signal C.sub.M separated by the digital comb filter 103, and outputs the switched luminance and chrominance signals to the video processing section 108. The video processing processing section 108 outputs the final RGB color signals to the CPT to display the color signals.
In the television system adopting a double window function, the tuner 104 receives and processes the RF signal received through the antenna ANT, and outputs the IF signal IF2 to the sub-channel IF processing section 105. The sub-channel IF processing section 105 processes the IF signal IF2, and outputs the composite video signal CVBS2 to the double window processing section 106.
The double window processing section 106 separates the composite video signal CVBS2 inputted from the sub-channel IF processing section 105 into the luminance signal Y.sub.P and the chrominance signal C.sub.P, and output the separated luminance and chrominance signals Y.sub.P and C.sub.P to the Y/C switching section 107.
The Y/C switching section 107 receives the luminance and chrominance signals Y.sub.M and C.sub.M from the digital comb filter 103 as well as the luminance and chrominance signals Y.sub.P and C.sub.P from the double window processing section 106, and output the final luminance signal Y and chrominance signal C to the video processing section 108 by switching the luminance signals Y.sub.M and Y.sub.P and the chrominance signals C.sub.M and C.sub.P, respectively.
The video processing section 108 combines the luminance signal Y and the chrominance signal C into the RGB color signals, and outputs the RGB color signals to the CPT, resulting in that a double-window picture is displayed on the CPT screen.
However, the conventional double window processing device has the drawback that when a viewer, for example, wishes to watch a main channel in an NTSC format and a sub-channel in a PAL format, or vice versa, the picture quality deteriorates due to the inconsistency of the synchronization between the main-channel and sub-channel pictures, which is caused by the different color systems when the double window function is performed for the main-channel and sub-channel pictures adopting the different color systems such as NTSC-M, PAL-M,N, etc.